Protein and alkali metal silicate adhesive



United States Patent 3,392,038 PROTEIN AND ALKALI METAL SILICATE ADHESIVE Alexander E. Tcyral, Mentor, Ohio, assignor to Diamond Shamrock Corporation, a corporation of Delaware Straight silicate adhesives do not meet these requirements. A number of mixed adhesives have been developed which are more highly water-resistant than straight silicate adhesives. For example US. Patent 2,894,847 describes a water-resistant protein-silicate adhesive which is prepared from a specific type of unhydrolyzed protein characterized by its freedom from carbohydrates, ligniferous matter, denaturation and hydrolysis products, and water-soluble materials. Suitable proteins for this purpose are those derived from soybean flour and sold by the Ralston Purina Company under the name of Industrial Protein and by the Buckeye Cotton Oil Company under the name of Buckeye Protein. According to the teachings of this patent, the desired adhesive contains no extraneous alkali other than that present in the silicate.

A principal disadvantage of the protein-silicate adhesives of the prior art, including those of US. Patent 2,894,847, is their short shelf life. These adhesives increase in viscosity on ageing even to the point of solidifying to a gel. This solidification often takes place within a very short time and their shelf life is usually limited to a day or so. Thus, they must be used almost immediately after mixing.

A principal object of the present invention, therefore, is to provide a water-resistant adhesive which is characterized by relatively little tendency to increase in viscosity with the passage of time.

A further object is to provide an adhesive with long shelf life, high water resistance and high bond strength.

Other objects will in part be obvious and will in part appear hereinafter.

It has previously been believed and taught by the prior art (e.g., US. Patent 2,681,290) that the presence of 3,392,038 Ce Patented July 9, 1968 extraneous alkali in protein-silicate adhesiveshas a detrimental efiect on bond strength. However, applicant has discovered that the presence of certain alkaline materials in certain restricted amounts does not adversely afiect bond strength. Moreover, the presence of these materials No Drawing. Filed Sept. 8, 1964, Ser. No. 395,051 5 improves the properties of protein-silicate adhesives in 13 Claimsthat it suppresses viscosity increase.

Accordingly, the adhesive composition of the present invention comprises (A) about 5% to 25% (preferably ABSTRACT OF THE DISCLOSURE l0-l2%) by weight of a high molecular weight, unhy- An unhydrolyzed vegetable protein-alkali metal silicate drolyzed vegetable protein, (B) about 10% to 30% adhesive composition has'its'use'ffitm preferably 20-25%) by weight of an aqueous alkali addition thereto of an alkaline material selected from the metal silicate with a silica to alkali metal oxide weight group consisting of alkali metal and am rn o niur r c ar; ratio bet 4.0:1, (C) an alkaline bonates and bicarbonates. At leas't'aportion of this alka- 15 material selected from the group consisting of alkali metal lifighizitfizilmusfbeadded at the initial stage of the and ammonium carbonates and bicarbonates in an amount formulation of the adhesive composition, from about 1% to about 10% by weight of the protein,

and (D) the balance water.

Liquid alkali metal silicates which may be used to form This invention relates to silicate-protein adhesives, and the adhesives of this invention are preferably sodium more particularly to adhesives used in the manufacture silicates, but may include silicates of the other alkali of boxboard and similar products, said adhesives being metals-that is, lithium, potassium, rubidium and cesium. characterized by low viscosity, long shelf life, high water They have a silica to sodium oxide weight ratio of beresistance and high bond strength. tween about 15:1 and 40:1 and a solids content between There has long been a need for low-cost water-resistant about and by weight. A number of suitable adhesives suitable for use in the manufacture of laminated sodium silicates are listed in Table I. products such as corrugated board, paper tubes, paper- TABLE I to-wood laminates and the like. Such adhesives have been P t so N O in particularly high demand in recent years for the manu- Grade men a- 3; Gravity, facture of boxboard for use in export shipment. Silicate 30 a Be. Seconds adhesives have been used for these purposes because of on en their low cost and the strong bond they produce. How- -9 9.1 29.2 38.3 3.22 41.0 15 ever, conventional silicate adhesives are not sufficiently 9,3 30,0 42,5 water-res stant to meet some of the more l'lgld specificag t g 10v 6 26.9 37 5 2 54 42.0 23 trons which have been recently drawn for paperboard mg 2.54 420 23 used in export shipment. In particular, United States it? 33:2 22:} 3% g g fig Government specifications require that such boxboard 47,3 240 510 640 shall have a high bursting strength not only when dry, 38 gig 1:3 5:3 1% but also after immersion for twenty-four hours in water. 12.4 32.1 44.5 2.58 49.0 '230 Among these silicates, Grade 33 is preferred.

The protein used in the adhesive composition of this invention is preferably that specified in US. Patent 2,894,847. This protein is derived from an oil seed flour, preferably soybean flour, by aqueous extraction at a pH between about 6.5 and 8, followed by adjustment of the pH to the isoelectric point of the extracted protein, whereby the desired protein fraction precipitates out of the aqueous solution. As pointed out hereinabove, a suitable vegetable protein is sold by the Ralston Purina Company as Industrial Protein and by the Buckeye Cotton Oil Company under the name of Buckeye Protein. Although other proteins may be used, the one specified hereinabove is advantageous in that it provides an adhesive which has a very high wet strength.

According to this invention, there is added to the adhesive made from the protein and silicate described hereinabove an alkaline material selected from the group con sisting of alkali metal and ammonium carbonates and bicarbonates, in an amount from about 1% to about 10%, preferably about 6-l0%, of the weight of protein present. Alkaline materials which are particularly suitable include sodium carbonate, sodium bicarbonate and ammonium bicarbonate; sodium bicarbonate is preferred.

Other r ie ch may be included in the adhesive include, for example, anti-foam agents, w, cross-linking agents and wetting agents. Pine oil is a typical preservative and anti-foam agent, and hexamethylenetetramine and urea are preferred crosslinking agents. These ingredients are preferably present in amounts between about 0.3% and 2% by weight. While a wetting agent is not essential, its presence in amounts up to about 0.1% may be advantageous in some cases. Other materials such as clays, triethanolamine and the like may be added to provide specialized adhesives for certain purposes.

A typical and preferred adhesive of the present invention is constituted as follows. (All percentages are by weight.)

Percent Protein 11.3 Grade 33 sodium silicate 22.5 Sodium bicarbonate (7% of weight of protein) 0.8 Pine oil 0.4 Hexamethylenetetramine 0.4 Water 64.6

The solids content of this adhesive is about 19%.

It is preferred that the viscosity of a protein-silicate adhesive be between about 4 and 16 poises. Whereas prior art adhesives have increased rapidly in viscosity with age, often attaining a viscosity of 40 poises or greater in one or two days, the adhesives of the present invention may be stored for 10 to days or longer without increasing in viscosity above about 16 to 18 poises. The actual viscosity increase will vary somewhat with the percentages of the various ingredients and the method of mixing of the composition. In particular, the percentage of alkaline material in the adhesive has a strong effect on viscosity and ageing qualities. It is important to note that, while the tendency of adhesives of the protein-silicate type is to increase in viscosity with the passage of time, this increase may not be constant and may even reverse itself. Thus, an adhesive may attain a maximum viscosity of the order of 30 to 35 poises within to 30 days, and the viscosity may then decrease to about 15 to 20 poises. However, the viscosity of the material should preferably not exceed 16 to 18 poises at the time of use.

In preparing the adhesives of this invention, the ingredients are added one at a time or in combination to the required amount of water, with stirring, at a temperature between about 70 and 125 F. In a preferred embodiment, the preservative (e.g., pine oil) and protein are introduced first in combination with all or part of the alkaline material (e.g., sodium bicarbonate). The mixture is then stirred for a few minutes after which the alkali metal silicate is added gradually, with constant stirring. Other ingredients are then added to provide the final product. While it is necessary to add at least a portion of the alkaline material at the beginning of the mixture sequence, along with the protein, not all of the alkaline material need be added at this time; a portion of it may be added at the end of the mixing operation along with or after other ingredients such as crosslinkers. Thus, for example, if the amount of alkaline material is 7% of the amount of pro tein in the adhesive mixture, 1-6% may be added at the beginning of the mixing process, and the remainder at the end. The final product desirably has a solids content between about 19% and 30%, the preferred range being 19-25%.

The adhesives of this invention may be used wherever a water-resistant adhesive is required in the manufacture of laminated products. Thus, corrugated paper board, plywood, paper tubes, paper to-wood laminates, metal foil-topaper laminates and the like may be manufactured with these adhesives. They are particularly useful, however, in the manufacture of corrugated boxboard. More particularly, water-resistant corrugated boxboard may be made by spraying cardboard liners and corrugated members with the adhesive according to the methods described in US. Patents 1,199,508 and 3,077,222. Alternatively, the adhesive need not be sprayed on the entire surface of the board but may be applied only to the tips of the fiutes of the corrugated members, whereby they are firmly attached by means of a water-resistant bond to the liner portions of the board. It will be apparent, however, that a more waterresistant board is obtained by spraying the entire surface of the corrugated portions with the adhesive than by merely coating the tips of the flutes therewith.

The bond strength of the adhesives of the present invention is tested in the following way. Samples of corrugated board are fabricated by applying the adhesive to the tips of the flutes of the corrugated member which is then glued to a liner member. The adhesive is set by applying pressure at a temperature of about 250-330" F. and is then aged overnight at i5 F. and a relative humidity of 601-12%. The force, in pounds, required to break the adhesive bond is then measured; this value is the drybond strength value.

An identical portion of board is soaked in water for 24 hours and is then aged in the same temperature-humidity environment as in the dry-bond strength test. The adhesive strength of the board thus treated is then measured; this is the wet-bond strength test.

Percent recovery is calculated by dividing the wet-bond strength by the dry-bond strength and multiplying the quotient by 100. Since increased adhesive penetration may be attained by contact with water, it is possible to obtain a percent recovery greater than It is desirable that weather-resistant boxboard have a wet-bond strength in excess of 50 pounds, and a recovery in excess of 75%. The adhesi'ies of this invention provide a board satisfying or exceeding these requirements. Further, the viscosity of these adhesives remains in a workable range for at least 30 days and often for 6-8 weeks; and the set time required for the adhesives is less than that for many adhesives of the prior art.

The invention is illustrated by the following examples.

Examples 1-6 A number of silicate-protein adhesive compositions are prepared by the following procedure. Water, 790 g., is heated to about 100 F. and a predetermined amount of sodium bicarbonate is added. Following the addition of the sodium bicarbonate, 4.75 g. of pine oil and g. of Industrial Protein is introduced. The mixture is stirred for three minutes. Grade 33 sodium silicate is introduced in two portions of 25 g. and 225 g. respectively, with five minutes of stirring between portions. After 19 minutes of stirring, a solution of 4.75 g. of hexamethylenetetramine in 7 ml. of water is added. Stirring is continued for an additional minute.

The final adhesive composition contains the following approximate ingredient percentages by weight. (The exact percentages for each ingredient will depend on the amount of sodium bicarbonate in the mixture.)

Percent Protein 10.5 Silicate (Grade 33) 21.0 Pine oil 0.4 Hexamethylenetetramine 0.4

The adhesive is aged for 41 days, with viscosity measurements being made at intervals. Results are given in Table II for compositions prepared by the above procedure and containing various amounts of sodium bicarbonate.

TABLE H NaHCOa, g. Viscosity (poises) with age (days) Example (percent of Protein) 1 7 14 21 31 41 As will be seen from Table II, a sodium bicarbonate content of 6-10% of the weight of the protein gives optimum viscosity values over a long ageing period.

Examples 7-11 Five adhesive compositions containing various amounts of sodium bicarbonate are prepared and aged according to the methods of Examples 1-6. Viscosity measurements are taken at intervals during the ageing process. After the indicated ageing period, the adhesives are used to make samples of boxboard by the following procedure. Adhesive is applied to the tips of the flutes of a corrugated member which is then adhered to a kraft liner. The adhesive is set at a temperature of 325 F. Dry-bond and wet-bond strengths are run on samples of board made by this procedure and percent recovery is 6 rapidly increases until it reaches a maximum of 40 poises, far above the useable range.

Example 18 The following example shows the effect of using other alkaline materials in the adhesive compositions of this invention.

An adhesive is prepared by the methods of Examples 1-6, with the following composition.

calculated. Sir G d 33 Pergin In Table III, the percentage compositions of the ade hesives of Examples 7-11 are given; Table IV gives vism cosity and bond strength results for these adhesives. Pme 011 Hexamethylenetetramine 0.4 Sodium carbonate 0.9 TABLE In Water 66.8 Example m 7 8 9 10 11 smcamomdesa) 2L2 no no no YISCOSHY measurements taken on this adhesive comp igrot b 1 g 13.2 10.5 10. 5 tron are given in Table VI.

ine 0.4 0.4 Hexamethylenetetramme-- 0.4 0.4 0.4 0.4 0.4 T E VI Sodium bicarbonate 0.2 0.4 0.6 0.1 0.8 Age, days: Viscosity, polses Water 67. 0 66. 9 5 1 L6 100.0 100.0 100.0 100.0 100.0 12 16.4 In these examples, the percentage of water includes about 0.08% o 21 Ultrawet DS," 2. sodium alkylbenzenesulfonate wetting agent added 31 in a 20% aqueous solution with the hexamethyleuetetramine. 42 6 5 TABLE IV N 111100;, Viscosity (poises) with age (days) Age (days) Dry-bond Wet-bond Percent Example D at time of strength, strength, Recovery Pw 1 10 0 Final testing lbs. lbs.-

2 0. 9 11.2 s. 3 s. 3 30 80 67 83 4 0. 0 11.6 s. 7 37 e0 56 81 6 5. 0 13. 6 12. 0 1 55 59 107 7 1.2 6.3 14 62 61 98 1. 5 1. 0 9. 0 19 66 57 86 It will be seen that all the samples tabulated in Table III have the properties desired for weather-resistant boxboard (50 lbs. wet strength, 75% recovery).

Examples 12-17 Adhesive compositions are made according to the method of Examples 1-6, except that a portion of the sodium bicarbonate is added at the end of the mixing process along with the hexamethylenetetramine. The over-all composition of the adhesives in these examples is as follows.

Percent Silicate (Grade 33) 23.6 Protein 11.8 Pine oil 0.5 Hexamethylenetetramine 0.3 Sodium bicarbonate (7% of weight of protein) 0.8 Water 1 63.0

1 Includes 0.08% Ultrawet DS."

Viscosity measurements taken during ageing of these adhesives are tabulated in Table V.

It will be seen from Table V that at least a small amount of alkaline material must be added at the beginning of the mixing process in order to attain the desirable results of this invention. When all of the bicarbonate is added at the end of the process, the viscosity This example shows that sodium carbonate is approximately equivalent to sodium bicarbonate in its effect on the viscosity of the protein-silicate adhesives.

It is to be understood that the invention is not limited by the specific examples and embodiments described hereinabove, but includes such changes and modifications as may be apparent to one skilled in the art upon reading the appended claims.

What is claimed is:

1. A method for stabilizing an adhesive composition, said composition comprising (A) about 5% to 25% by weight of a high molecular weight, unhydrolyzed vegetable protein, (B) about 10% to 30% by weight of an aqueous alkali metal silicate with a silica to alkali metal oxide weight ratio between about 1.5 :1 and 40:1, and (C) the balance water, which method comprises adding from 1% to 10% by weight, on a protein basis, of an alkaline material selected from the group consisting of alkali metal and ammonium carbonates and bicarbonates and which method is characterized by adding at least a portion of said alkaline material, with stirring, to the protein prior to the addition of said silicate.

2. A method for the preparation of an adhesive composition which method comprises the steps of:

(a) mixing about 5 percent to 25 percent by weight, on a total adhesive basis, of a high molecular weight, unhydrolyzed vegetable protein, about 1 percent to 10 percent by weight, on a protein basis, of an alkaline material selected from the group consisting of alkali metal and ammonium carbonate and bicarbonates and water and,

(b) adding, with mixing, about 10 percent to 30 percent by weight, on a total adhesive basis, of an aqueous alkali metal silicate with a silicon dioxide to alkali metal oxide weight ratio between about 15:1 and 4.0: l,

the balance of said composition being water.

3. A method as in claim 2 wherein only a portion of 7 a the alkaline material is added in step' (a), the remainder being added in step (b).

4. A method as in claim .2 wherein from 0.3-2% by weight of a preservative is added in step (a).:

5. A method as in claim 2 wherein from 0.3-2% by weight of across-linking agent is added in step '(b). V

6. A method as in claim 2 iwherein up to about 0.1% by weight of a wetting agent is added in step (b).

7. A product as produced by the method of claim 2.

8. The method for the preparation of an adhesive composition of claim 2 wherein the protein is one which is derived from soybean flour by aqueous extraction at a pH between about 6.5 and 8 followed by adjustment of the pH to the isoelectric point of the extracted protein, whereby the desired protein fraction precipitates out of the aqueous solution. 1

9. The method for the preparation of an adhesive composition of claim 2 wherein the aikali metal silicate is sodium silicate. r

10. The method for the preparation of an adhesive composition of claim 2 wherein the alkali metal silicate is a sodium silicate and has a silica to sodium oxide weight ratio of 3.30:1, a solids content of 37.9 percent and a Be. gravity of 41.0.

11. The method for the preparation of an adhesive composition of claim 2 wherein the alkaline material is sodium bicarbonate.

12. A method for the preparation of an adhesive composition which comprises the steps of;

(a)'mixing about 5 to 25 percent, on a total adhesive I bonates and bicarbonates, 0.3 to 2 percent on a.

percent References Cited UNITED STATES PATENTS 1,950,060- 3/1934 Osgood -2 10679 1,976,435 10/1934 Cone et al. 10679 2,457,108. 12/1948 Baker et al. 10679 2,894,847 7/1959 Wright 10679 3,058,835 "10/1962 Sheeran l0679' 3,206,320 9/1965 Davidson 10616l 3,206,321 79/1965 Davidson 106-161 3,274,042 9/1966 Gilboe et al 106-154 TOB IAS E. LEVOW, Primary Examiner; S. E. MOTT, Assistant Examiner. 

